1. Field of the Invention
The present invention relates to digital data readout devices and more particularly to apparatus for coupling digital data generators to digital data readout devices.
2. Description of the Prior Art
Step data gyrocompasses provide heading information by generating electrical output signals in the form of three phase displaced pulse modulated sixty or four hundred cycle signals. These pulse modulated alternating current signals are full wave rectified and the resulting pulses are coupled to a digital data readout device wherein they are processed and a visual representation of the heading is provided. Prior art methods of providing this digital data to the readout device, either directly coupled the data thereto or employed an attenuating coupler between the step data gyrocompass output terminal and the readout device without providing electrical isolation therebetween. State level switching in the readout device due to these rectified pulses, occurs when the leading edge crosses a given threshold and internal system noise, such as that caused by differential ground currents between the step data gyrocompass and a remotely located digital data readout device, may cause erratic processing of the compass step data and erroneous heading indications. To eliminate this erratic operation, it is required to provide electrical isolation between the gryocompass and the readout device and to establish a range within which switching is not accomplished. This range may be realized by providing switching action with hysteresis, that is, a first threshold level for switching from one logic state to another and providing a second threshold level for switching back.
It is the object of the present invention to provide a coupling device between a digital data generator and a digital data readout device to provide electrical isolation therebetween and to establish a first threshold level for switching from a first logic state to a second logic state and a second threshold level for switching from the second logic state to the first logic state.